1. FIELD OF THE INVENTION
The present invention relates to a novel photographic color coupler, a photographic light-sensitive material containing such a coupler and a method of forming an image using such a coupler.
2. DESCRIPTION OF THE PRIOR ART
It is well known that an oxidized aromatic primary amine developing agent reacts with a dye forming coupler to form a color image by color development after exposure of a silver halide photographic light-sensitive material to light. In this method, a color reproduction process according to the conventional subtractive method is employed to form a cyan, magenta or yellow color image which is in a complementary relation with the red, green or blue color. For instance, a phenol derivative or a naphthol derivative is used as a coupler for forming a cyan color image. The reaction of a coupler with a color developing agent is carried out at the active position of the coupler. Couplers having hydrogen atoms at the active position are four equivalent couplers, that is, they theoretically stoichiometrically require four moles of exposed silver halide as an oxidizing agent for the formation of one mole of dye. On the other hand, couplers having a group capable of being released as an anion at the active position of the coupler are two equivalent couplers, that is, they require only two moles of exposed silver halide for the formation of one mole of dye. Such two equivalent couplers generally provide advantages in comparison with four equivalent couplers. For example, the sharpness of the color images formed is improved. Further, the processing time of the light-sensitive material is reduced because of the decrease in the thickness of the emulsion layer due to the reduction in the amount of silver halide in the emulsion layer. Examples of such releasable groups are a sulfonamido group as described in U.S. Pat. No. 3,737,316, an imido group as described in U.S. Pat. No. 3,749,735, a sulfonyl group as described in U.S. Pat. No. 3,662,328, an aryloxy group as described in U.S. Pat. No. 3,476,563, an acyloxy group as described in U.S. Pat. No. 3,311,476 and a thiocyano group as described in U.S. Pat. No. 3,214,437.
Further, appropriate modifications of the releasable group are also known. For example, a coupler having a releasable group including a diffusible dye moiety is useful in a diffusion transfer process in which a diffusible dye released from the coupler is used to form a dye image in an image receiving layer. Such couplers are designated diffusible dye releasing couplers and are described, for example, in U.S. Pat. Nos. 3,227,550 and 3,765,886, U.S. Patent Defensive Publication T 900,029 and British Pat. No. 1,330,524.
Furthermore, certain colored two equivalent couplers have masking effects for color correction of dye images. Such couplers are designated colored couplers and are described, for example, in U.S. Pat. No. 3,476,563.
Further, a two equivalent coupler which releases a compound having development inhibiting effects is designated a development inhibitor releasing coupler (DIR Coupler). Such a coupler controls development in proportion to the extent of development and thus is effective in reducing the graininess of the developed image, controlling the gradation of the image and improving the color reproducibility. Also, such as coupler can be used in a diffusion transfer process using the effects thereof on an adjacent layer. Examples of such couplers are described in U.S. Patent 3,227,554, Japanese Patent Application (OPI) 122,335/1974 and German Patent Application (OLS) 2,414,006.
As described above, two equivalent couplers have substantial advantages and various applications in comparison with four equivalent couplers, and, thus, they are used to a greater extent.
However, most two equivalent couplers which are known have the disadvantages that their coupling reactivity is insufficient, marked color fog is produced, dispersibility is poor (resulting in difficulties in coating), the coupler per se is unstable and cannot be stored for long periods of time, the stability during storage of color images formed therefrom on color development is poor and the like. Therefore, overcoming such disadvantages has been desired.
Further, when the DIR couplers described in U.S. Pat. No. 3,227,554 are used, during color development, strong development inhibiting effects occur only at a developing center of the silver halide (an aggregate of latent image nuclei) and which are very effective for reducing the graininess of image. On the other hand, they have defects such as decreasing gradation (gamma) and decreasing maximum color density (D.sub.max) and do not provide interlayer effects which are desirable for color reproduction in multilayer color light-sensitive materials.
Therefore, couplers which have appropriate development inhibiting effects in a layer and can provide strong interlayer effects have been desired from the standpoint of color reproduction.
Furthermore, most couplers described in U.S. Pat. No. 3,227,554 are unstable and thus greater attention must be paid during the production of the color light-sensitive materials and storage of fresh light-sensitive materials.